Carburetor



May 2, 1944. s. F. HUNT CARBURETOR Filed March 51, 1941 III I I Illilllh Awawrae Staff F. f/um" PatentedMay 2, 1944 CARBURETOR Scott F. Hunt, Meriden, Conn., asslg'nor to Chandler-EvansCorporation, a corporation of Delaware Application March 31, 1941, Serial No. 386,019

My invention relates to carburetors.

It has among its objects to provide an improved carburetor of the type utilizing a variable pressure fuel pump, and, more particularly, to provide such a carburetor having improved means for so controlling the pump pressure as to minimize the formation of vapor during the operation thereof. A further object of my invention is to provide such an improved carburetor having a regulator and improved means for maintaining a predetermined differential between the regulator pressure and the pump pressure whereby, within limits, the regulator is rendered insensitive to variations in pump pressure or speed, at the same time that a minimum drop in pressure throughout the system is made possible. Still another object of my invention is to provide such improved controlling mechanism adapted to obtain the above advantages while the regulator varies the fuel pump discharge pressure in accordance with variations in air flow. A still further object of my invention is to provide improved means whereby, as a result of a simple and inexpensive change in the connections of a carburetor of the type having a regulator controlling the pump discharge pressure of a constant pressure fuel pump, the latter is converted into a variable pressure pump while also being controlled in accordance-with my invention. These and other objects and advantages of my improved construction will, however, hereinafter more fully appear.

In the accompanying drawing, I have shown for purposes of illustration one embodiment which my invention may assume in practice, a carburetor system constructed in accordance with my improvement being shown in diagrammatic form therein.

In this illustrative construction, the carburetor is of the general construction described and claimed in a co-pending application of Milton E. Chandler, Serial No. 474,575, filed February 3, 1943, which is a continuation of application Serial No. 386,046, filed March 21, 1941. As shown in said application, I have illustrated an air flow Venturi mechanism I having a throat 2 and scoop 3 and valve mechanism including a diaphragm valve 4 and a plunger 4a acting on one side of said diaphragm and having a spring 5 biasing the diaphragm to valve closing position; this plunger being controlled by diaphragm 4 and a diaphragm 6 carrying the plunger and, both diaphragms being subject to throat pressure in a chamber 1, while scoop pressure also acts on the opposite side of diaphragm 6 in a chamber 8.

5 Claims. (Cl. 261-27) As in that construction, the diaphragm valve 4 also acts to vent the fuel flowing in a pipe 9 and in a chamber III, on the opposite side of diaphragm 4, to a port l2 and a vent l3 in accordance with variations in air flow through the venturi, while a pressure responsive mechanism I4, responsive to scoop pressure and the temperature in a tube I4a. varies the opening and closing movements of the valve 4 in accordance with variations in altitude and temperature. As in said Chandler construction, fuel from a tank I5 is also supplied through a pump it to a vapor trap and filter mechanism, generally indicated at IT, and having a vapor return connection Ila to the tank l5, while fuel is also supplied from the mechanism I! through a regulator mechanism generally indicated at 26, to a manually operated mixture controlling valve l8 controlling the fuel flow through parallel fixed orifices l9 and a parallel spring loaded power jet 20, to a main metering orifice 2| from which the fuel passes through a compensator valve 22 to a nozzle 23 downstream from throttles 24 movable with an idling valve 25. Further, as in that construction, a regulator mechanism, generally indicated at 28, is provided between the vapor trap and filter mechanism I! and the valve I 8, which includes a regulator valve 21 longitudinally reciprocable in a ported valve" casing 28 by a diaphragm 29 adjustably biased to valve opening position by a coiled spring 30 acting on the bottom thereof. As in that same construction, fuel flowing from the mechanism I! through a pipe l'lb, enters a chamber 3| surrounding the valve 21 and passes.through ports 21a, 21b in the easing into a chamber 32 above the diaphragm 29 and also passes out of said chamber 32 through a passage 33 leading tothe valve I 8, while a chamber 34 on the underside of diaphragm 29 communicates with the upper chamber 32 through a restricted passage 35 and the chamber 34 also communicates with the pipe 9 through which the flow of fuel is controlled by the valve 4 in accordance with variations in the diflerential of pressures in the throat2 and scoop 3.

In my improved construction, however, instead of utilizing a constant pressure type pump I B, the same is transformed into a variable pressure pump at the same time that a predetermined difference between regulator pressure and pump pressure is maintained. Herein these results are produced by providing a new pipe'connection 36,

between the chamber 32 and a chamber 3'! above a pump by-pass controlling diaphragm 38 which,

in turn, controls a by-pass valve 39 of pump I6 and is subject to pump discharge pressure passing through a port 49 in this by-pass valve 39. As shown, this connection 38 is made to the pipe 33 leading from the chamber 32 to the valve 18, but obviously it may be made directly to the chamber 32 if desired, while the' opposite end of this connection opens through the top of an upper casing member 4l housing the diaphragm 38 and an adjustable biasing spring 42. Thus, with a chamber 43 beneath the diaphragm 38,

responsive to pump discharge pressure, the

chamber 31 above the diaphragm is responsive to variations in fuel pressure in the pipe 33 and chamber 32. As a result, if the spring 30 is set to maintain a given pressure in the chamber 32, as, for example, a three pound pressure, and if the spring 42 is set to maintain a given larger pressure in the chamber 43, as, for example, a five pound pressure, this pressure differential will be maintained by reason of the connection 36, throughout the operation of the mechanism.

In the operation of my improved construction, the regulator 26 will operate as heretofore, in such manner as to vary the fuel pressure in the chamber 32, and, consequently, the fuel fiow delivered through the orifice 2| and nozzle 23 will be varied proportionally with variations in the differential of throat and scoop pressures existing in the chambers I and 8; the valve 21 being opened further to increase the fuel fiow in proportion to any increase in air flow through the venturi, all as described and claimed in the above mentioned Chandler application. However, in my improved construction and by reason of my new connection 36, the pump l6 instead of operating to maintain a substantially constant discharge pressure, will operate as a variable pressure pump, with the pump discharge pressure varying proportionally as the quantity of air flow varies. Further, it'will be observed that, due to the connection 36, any change in pressure in the chamber 32 above the diaphragm 29 will be transmitted to thechamber 31 above the diaphragm 38 controlling the by-pass valve 39 of the pump 16. Thus, as the fuel pressure in chamber 32 is increased inresponse to increased air flow and opening movement of valve 21, the pressure in chamber .32 will supplement the pressure of spring 42 on the pump diaphragm 38 in such manner as to tend to maintain the pump by-pass valve 39 closed and thereby develop a higher pump discharge pressure proportional to'the increase in air fiow. Moreover, it will be observed that, with the regulator spring 30 set to maintain a given pressure in the chamber 32 lower than the pressure maintained in the chamber 43 by the setting of the spring 42 of the pump, this difference in pressure willbe maintained throughout the whole range of operation of the carburetor. For example, with spring 42 exerting a pressure of two pounds more than spring 30, when there is a discharge pressure of 28 pounds in the regulator chamber 32, the pump discharge pressure will be 30 pounds, 1. e.'the same pressure as in the regulator, plus the increased load of 2 pounds on the pump by-pass valve controlling spring 42, while, when the regulator pressure drops, the pump discharge pressure will also drop but always remain 2 pounds higher than the regulator pressure.

As a result of my improved construction, it is made possible for the variable pressure fuel pump to develop a high discharge pressure without causing the substantial vapor formation hereto-- fore characteristic of fuel pumps of the relief valve type. In my improved'construction, whil the pump discharge pressure has the same range as heretofore, the fuel in the pump discharge is never delivered into a substantially lower pressure chamber in the regulator, in such manner as thereby to effect the release of vapor, the objectionable formation of vapor in either the pump or the regulator beingthus minimized. Instead, the regulator pressure and the pump pressure are always maintained in a predetermined relation with only the predetermined difference determined by the difference in settings of the springs 30 and 42, forexample, a pressure difference of 2 pounds, which is insufiicient to cause objectionable vapor release. Further, due to my improved connection 38', it will be observed that the regulator becomes relatively insensitive to changes in pump pressure or speed within limits, while it will also be observed that it is made possible to maintain a minimum drop in pressure throughout the system and that pulsations are minimized by the air dome provided in the closed spring chamber in the member 4|.

While I have herein specifically described one form which my invention may assume in practice, it will be understood that this form has been shown for purposes of illustration and that my invention may be modified and embodied in other forms without departing from its spirit or th scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. In a fuel supply system for an internal combustion engine, in combination, a first conduit for conveying air for combustion purposes to said engine, means in said first conduit for producing two unequal pressures therein whose difference is a measure of the quantity of air flowing therethru, a fuel pump, a second conduit for conveying fuel from said pump to said engine,

a metering restriction in. said second conduit,

first valve means in said second conduit downstream from said restriction for maintaining a minimum pressure therein, second valve means in said second conduit forcontrolling the pressure difierentialacross said restriction, first diaphragm means for operating said second valve means in response to the, difference of said two unequal pressures;by-pass valve means for controlling the fiow of fuel from the outlet to the inlet of said pump, second diaphragm means for operating said by-pass valve means, a connection for transmitting the pump outlet pressure to one side of said second diaphragm means and a second connection for transmitting the pressure in said second conduit downstream from said second valve means to the other side of said second diaphragm means so that said by-pass valve means is operated to maintain a substantially constant pressure drop across said second valve means, spring means associated with each of said diaphragm means for biasing its associated valve means, and means for adjusting each of said spring means so as to control the magnitude of the pressure drop across said second valve means.

2. In a fuel supply system for an internal combustion engine in combination, a first conduit for conveying air for combustion purposes to said engine, means in said first conduit for producing two unequal pressures therein whose difference is a measure of the quantity of air flowing therethru, a fuel pump, a second conduit for conveying fuel from said pump to said en e. a metering restriction in said second conduit, valve means in said second conduit for controlling the pressure diflerential across said restriction. first diaphragm means for operating said valve means in response to the difference of said two unequal pressures, by-pass valve means for controlling the flow of fuel from the outlet to the inlet of said pump, second diaphragm means for operating said by-pass valve means, a connection for transmitting the pump outlet pressure to one side of said second diaphragm means, and a connection for transmitting the pressure in said second conduit downstream from said valve means to the other side of said second diaphragm means, so that said by-pass valve means is operated to maintain a substantially constant pressure drop across said valve means, spring means associated with each of said diaphragm means for biasing its associated valve means. and means for adjusting each of said spring means so as to control the magnitude of the pressure drop across said second valve means.

3. In a fuel supply system for an internal combustion engine, in combination, a first conduit for conveying air for combustion purposes to "said engine, means in said first conduit for producing two unequal pressures therein whose difference is a measure of the quantity of air flowing therethru, a fuel pump, a second conduit for conveying fuel from said pump to said engine, a metering restriction in said second conduit, valve means in said second conduit for controlling the pressure diiferential across said restriction, first diaphragm means for operating said valve means in response to the difierence of said two unequal pressures, by-pass means for controlling the flow of fuel from the outlet to the inlet of said pump, second diaphragm means for operating said bypass means, a connection for transmitting the pump outlet pressure to one side of said second diaphragm means, and a connectign for transmitting the pressure in said second conduit downstream from said valve means to the other side of said second diaphragm means so that said bypass means is operated to maintain a substantially constant pressure drop across said valve means, spring means associated with each of said diaphragm means and acting on its associated valve means, and means for adjusting the force of at least one of said spring means so as to control the magnitude of the pressure drop across said valve means.

4. In a fuel supply system for an internal combustion engine, in combination, a first conduit for I conveying air for combustion purposes to said engine, means in said first conduit for producing two unequal pressures therein whose difference is a measure of the quantity of airfiowing therethru, a fuel pump, a second conduit for conveying fuel from said pump to said engine, a metering restriction in said second conduit, valve means in said second conduit for controlling the pressure differential across said restriction, first diaphragm means for operating said valve means in response to the difierence of said two unequal pressures, by-pass means for controlling the flow of fuel from the outlet to the inlet of said pump, second diaphragm means for operating said bypass means, a connection for transmitting the pump outlet pressure to one side-of said second diaphragm means, and a connection for transmitting the pressure in said second conduit downstream from said valve means to the other side of said second diaphragm means so that said by pass means is operated to maintain a substantially constant pressure drop across said valve means and spring means associated with each of said diaphragm means for biasing its associated valve means, the magnitude of the pressure drop across said valve means being determined by the characteristics of said spring means.

5. In a fuel supply system for an internal combustion engine, in combination, a first conduit for conveying air for combustion purposes to said engine, means in said first conduit for producing two unequal pressures therein whose difference is a measure of the quantity of air flowing therethru, a fuel pump, a second conduit for conveying fuel from said pump to said engine, a metering restriction in said second conduit, valve means in said second conduit for controlling the pressure difierential across said restriction, first diaphragm means for operating said valve means in response to the diflerence of said two unequal pressures, by-pass means for controlling the flow 01' fuel from the outlet to the inlet of said pump, second diaphragm means for operating said by-pass means, a connection for transmitting the pump outlet pressure to one side of said second diaphragm means, and a connection for transmitting the pressure in said second conduit downstream from said valve means to the other side of said second diaphragm means so that said by-pass means is operated to maintain a substantially constant pressure drop across said valve means, and spring means associated with said sec- 0nd diaphragm means and acting to move its associated by-pass means in a flow decreasing direction, the magnitude of the pressure drop across said valve means being determined by the characteristics of said spring means.

SCO'I'I' F. HUNT. 

